Welding backup assemblies provide a variety of functions in electric welding processes. Backup assemblies may be used to seal an opposing side of the workpiece to prevent or diminish oxidation of the workpiece. Backup assemblies may also be used to catch molten metal, thereby assisting in the welding process. Backup assemblies may further be used to roughly shape or smooth the backside of the weld, thereby eliminating or substantially reducing post-weld treatments, such as grinding.
"Backing" or "backing-up" or similar words are intended to refer to the position of a welding tape assembly adjoining and covering one side of a joint to be welded opposite another side of the joint on which an active welding electrode is applied.
U.S. Pat. No. 3,365,566 describes several welding backup tape assembly variations. In one embodiment, an elongated continuous piece of metallic foil is provided with adhesive surfaces along its edges on one side to allow the foil to be adhered to a workpiece with a clean, central portion of the foil backing the joint to be welded. Another embodiment is provided by a flexible layer or ribbon of a heat-resistant material, such as glass cloth, having an adhesive surface and a narrower thin metallic layer or foil, preferably a copper or aluminium alloy, adhered to the adhesive surface on one side of the ribbon, centrally disposed on the ribbon to expose edge portions of the adhesive surface of the glass cloth layer for adhering the tape assembly with the metallic layer or foil backing the joint to be welded. In yet another embodiment, the flexible metallic strip and glass cloth are reversed.
One particular embodiment of U.S. Pat. No. 3,365,566, depicted in FIG. 14, is particularly relevant to the subject invention. In that embodiment, a filler in the form of a cord is provided between an adhesive surface of a flexible metallic strip and an overlying woven glass fiber strip of narrower width, adhered to the surface of the metal strip to provide additional backup. The precise manner of retaining the cord between the layers is not disclosed. While the cord may also be adhered to the metallic strip with the woven glass fiber strip, there does not appear to be any connection between the cord and either strip, other than friction and possibly an adhesive, which would assist in keeping the assembly together if it were to be grasped by the cord for removal. Also, the provision of the woven glass fiber strip to protect and/or attach the cord to the metal foil strip increases the number of components and thus the cost of the assembly.
Another known welding backup tape assembly includes an elongated metal foil strip supporting a bead of ceramic (e.g., aluminum oxide) granular elements conglomerated by means of a binder. Peel away strips protect a pressure sensitive adhesive on the foil to either side of the granular bead. It also has some drawbacks. First, the granular bead is moisture absorbing. The assembly must be stored in a poly bag to prevent moisture pick up and must be dried for hours at an elevated temperature before use if the assembly becomes moist from exposure. Some portion of the surface ceramic grains are usually trapped in the surface of the weld. This may necessitate grinding to remove the grains and/or provide a smooth surface. Lastly, the binder may smoke under certain welding conditions from the heat generated. This may be an irritant to the welders and may obscure their vision of the workpiece.
Lastly, another type of welding backup tape assembly is disclosed in U.S. Pat. No. 4,182,951. The assembly of this patent includes an adhesive coated mounting strip, preferably of a metallic foil, which receives and retains one or more molded ceramic elements. The latter are positioned against the workpiece opposite the joint to be welded. This patent has the same inventor, B. A. Kuder, as aforesaid U.S. Pat. No. 3,365,566. Mr. Kuder states in his U.S. Pat. No. 4,182,951 that the ceramic carrying welding backup tape assemblies of that patent are an improvement over his earlier welding backup tape, which could suffer burnthrough of the heat resistant fibrous material (i.e., the glass cloth) during heavy welding applications. This type of assembly affords improved performance over both the tape on tape assembly of U.S. Pat. No. 3,365,566 and the other, known conglomerated ceramic bead tape assemblies. However, the significantly greater costs of this design encourage the use of less expensive backup assemblies, like the first two discussed, whenever possible.